Electroluminescent image device



Dec. 3l, 1957 s. c. PEEK, JR- f A 2,818,531

ELECTROLUMINESCENT IMAGEV DEVICE Y' Filed June 24, 1954 i-.fm n F1 g'. 2

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ATgroRNEY United States Patent 'C ELECTROLUMINESCENT IMAGE'DEVICESandford Christopher Peek, Jr., South Hamilton,`Mass., assignor toSylvania Electric Products Inc., Salem, vMass., acorporation ofMassachusetts Application June 24,1954, SerialjNo. 439,018

9 Claims. (Cl. 315-166) This invention relates to the production ofimages, and especially .of varying images, in an electroluminescentmaterial.

.Such images can be produced in an electroluminescent phosphor layerwhich has a series of conducting lines on one side of it 'and anotherseries of such lines ,on the other, the two series being at an angle toeach other, the angle `preferably being 90. At least one of the seriesof conducting lines is preferably made of light-transmitting conductingmaterial.

If .a voltage source is connected between one line on one side ofthephosphor layer and another line on the other side, the phosphor shouldluminesce in the neighborhood of the point where they cross. Thecapacity effects between wires, however, are generally such that notonly the cross-over point, but also several of the wirecrossing pointsaround the point where the actually live wires or conductors crossluminesce in addition, .thereby producing halation and reducing thesharpness of the image, if not completely obscuring it.

I have found that the luminous spot can be confined to the point wherethe two live wires cross, if-therwires include a rectifying layer orcoating on and in series with eachof kthe wires of one series, withpreferably a set of such rectiers for each series.

ln order to allow the luminous spot to be shifted from point to point inthe phosphor layer in response to a received signal, and varied also inamplitude according to that signal, the wires of one series can beconnected to different points along a delay line, and the wires of theother series connected to different points on another delay line. Thenif a direct current bias is used in series with the rectitiers, andadjusted so that the voltage across the phospho-r layer is a fixed valuebelow that required for electroluminescence, and a pulse sent along eachdelay line, the sum of the voltages of said pulses Ibeing equal to saidfixed value, then in response to 'an additive series signal there willbe no electroluminescence at a given instant except at the cross-overpoint of the two wires on which the pulse voltage exists at thatinstant, as long as the signal is of smaller voltage than the sum of thepulse voltages. The signal will thus only be effective at a particularpoint at a particular instant, and if 4thc signal is in synchronism withthe pulses, a desired image can be reproduced from the signal onto thelphosphor layer, by successively illuminating different points at thesame or different intensities.

The sum of the two pulses does not have to be equal to the voltagenecessary to excite the `phosphor to the threshold of luminescence; itcan be somewhat below that value, if desired, and the signal amplitudechanged accordingly, especially if the signal is D. C. The signalvoltage can be alternating, and of a frequency sutiiciently above thefrequency of the pulses as to avoid interfering with the pulses. Inother words, the alternating current is similar to a carrier frequencyfor the signal; the

amplitude of the alternating current is modulated to produce .thesignal. The phosphor layer can be a layer containing a lmixture ofphosphor .particles and solid vdielectric material, for example avphosphor .particle yembedded -in a dielectric material. If thedielectric .material ;is omitfarice ted,the ,conductive lines can be indirect .contact with'the phosphorparticles and in .that .case the signalvoltage 'can be modulated direct current, instead of alternatingcurrent.

Other advantages, features and objects of the` invention will :be`apparent .from the following specification taken in connection with theattached drawing in which:

Figure l is a schematic 'circuit .diagram `of 'one embo'climent o'f my.device; and

.Figure 2 is a cross-sectional view of the electrolumin'escent portionof the device.

In Figure l, the electroluminescent phosphor layer 1 has the series .2,4, 6,8, etc., of Wires running'vertically on one side of the layer 1,and theother series 3, 5, 7,'9 running horizontally on the other side ofthe layer 1. The l-atter series is connected respectively to therectiiers v13, 15, 17, .19, etc., and through them tothe condensers 24,25, 26,29, etc., and through them to the biasing voltage 11. Inductioncoils 30, 31, 32, 33, 35, etc., are connected between each condenser 13,15, 17, 19, and between the terminal resistance 11 and the pulsetransformer 20, so the combination forms a delay line, properlyterminated in resistance 11, and fed with voltage pulses from the pulsetransformer 26.

The battery 10 is in series with the common terminal 21 of the delayline so formed, and the signal transformer 36 is .also in series, as isthe common terminal Y33 of the delay line formed by the condensers 22,24, 26, 28 and vthe choice coils .38, 39, 40, 41, 42, together with theterminal resistor 43 and the input pulse transformer 44 lfor feeding theline. The condensers 22-`28, connected at one uend of each to the commonterminal 33 are connected at the other ends to the .conductors 22-28through the rectitiers 12-18, condenser 22 being connected to rectifier12 and to conductor 2, condenser 24 being connected to rectiier 14 andterminal 4 and so forth.

.In Fig. 1, .the circuit shown has the rectiers in the ,circuit externalto the lamp, in order that the function of the rectiiiers with respectto the pulses and bias could be explained more clearly. The externalrectiers have the advantage of allowing the use of a bias voltage tokeep Ythe applied signal voltage off the wires'except for the two onwhich pulses are applied at a particular instant.

The use of ya rectifying coating or layer 52 as in Fig. 2, and asrepresented by the dotted lines in Fig. l, which also indicate lthecapacity between wires, eliminates the need for the external rectiliersand gives the same effect, but in addition reduces the halation due tocapacity effects between wires. The capacity between `cross-overs at 51,70, and 71 would, in series, be connected across the capacity at 52, andluminesce at reduced intensity, except that at least one of therectifying layers at Vthe cross-overs would be in the back-direction andhold olf the voltage.

The electroluminescent layer 1 and its immediate surroundings are shownin further detail in the cross-sectional view lof Figure 2. Theconductor 4 is shown fixed to the glass front piece 45. Theelectroluminescent layer 1 is shown over conduct-or 4 and the otherconductors 3, 5, 7, 9, are shown over the electroluminescent layer. Therectiers 12-18 and 13-19 of Figure l can be separate from thelconductors 2 8 and 39, but if desired `they can be formed on the backof conductors 2-8 and/or 3 9, as shown in Fig. 2. If the conductors 3-9,for example are of aluminum, .selenium rectifying layers .S3-5.7 can beformed on the aluminum in the manner customary :in the seleniumrectifier art, and then the counter-electrodes 63-67 placed over them,respectively. Several selenium rectiiiers in series may be required tostand the voltage used -on the electroluminescentlayer.

The various electrodes vmay be sprayed onto the electo give the desiredpattern, and the electrons 2 8 can be sprayed directly on the glassplate 45 if desired. Either one or both sets of electrodes should be ofconductive glass to permit light transmission therethrough, the lowerelectrodes 2 8 being preferably light-transmitting in the ligure.

The various parts of the electroluminescent layer and its associatedelectrodes can be made up as shown for example in copending patentapplication, Serial No. 365,617, filed July 2, 1953 by Richard M. Rulon.

In operation, the battery 11 biases the rectiers, and the sum of thepulses received by the lines from pulse transformers 20 and 44- issuicient to remove the bias to bring the rectiers up to the voltage atwhich they pass current, and to bring the electroluminescent lamp up atleast to the vol-tage threshold of its luminescent curve.

When the Signal is introduced by the signal transformer 36, it willcause the electroluminescent layer 1 to luminesce at the point where thewires carrying the pulse at that instant cross The wires do not actuallytouch of course, because the two series of wires 2 -3 and 3 9 are onopposite sides of the electroluminescent layer.

For example, suppose the pulse from transformer Z is at a particularinstant on wire 7, and the pulse from the other transformer 44 is at thesame instant on wire 4, then the cross-over point 50 of these two wires4, 7 will be made luminous by the additional voltage from signaltransformer 36, and its brightness will depend -on the `signal voltageof that transformer at that instant.

An instant later, the pulse from transformer 44 will have moved to wire7 while the slower pulse of transformer will still remain on wire 6;accordingly, point 51 will light up, and of course next point 52, andthen point 60.

A new pulse will then start out from pulse transformer, and travel fromwire 2 toward wire 8; but now the longer and slower pulse Ioftransforme-r 20 will have moved downward to wire 5, so that points 61,62, 70, 71 and 72 will now be illuminated in turn.

A new pulse from transformer. 20 will then start out 'on line 3, and theprocess be repeated along that conductive line.

lt is clear that the pulse from transformer 20, which we may call thevertical pulse for convenience, must 'be longer than that fromtransformer so that it will be effective on a single horizontal wireuntil the pulse from the latter transformer goes from. Wire 2 to wire 8,and that the pulse must travel more slowly so that it will, for example,move only from wire 2 to wire 5 while the pulse from the othertransformer goes from wire 2 to Wire S.

Although for convenience only 4 conductors are shown on one side of theelectroluminescent layer 1 and 5 on the other side, any number desiredfor a given type of image may be used. For example, 500 lines per sidemight be used, as in television. That would require `a delay line rofmany sections, unless the line was made up of a long cylinder and thewires tapped ofl at different points along the cylinder.

The rectifying layers such as 5.5 57 in Fig. 2, are shown only on theelectrodes on one side of the electroluminescent layer 1, vbut arepreferably used on the 'conductors 2 8 on the `other side also.

Another form of electroluminescent image device can be made by using onetransparent electrode of continuous surface on one side of anelectroluminescent layer such as 1, and a mosaic of separate points ofphotoresistive or photoconducting material, such as selenium, on theother, with the points of the mosaic in contact with a transparentconductive layer. An image could then be focussed onto the mosaic andwould appear in amplied form on the yelectroluminescent layer, theresistance of the dierent points of the mosaic being dependent on thebrightness age across the electroluminescent layer, a fixed voltagebeing applied between the two transparent conductive plates.

In Fig. 2, the conductors 3, 5, 7, 9, are linear conductors extendingfrom one side to the other of the active portion of theelectroluminescent layer 1, just as conductors 2, 4, 6, 8, etc., do inFig. 1. Conductors 63-67 `as shown in Fig. 2, however, do not extend allthe way across the electroluminescent layer, but are broken between thecross-over points, so that they exist only as a series of separatedareas over each cross-over point. This is necessary in order to forcethe current to go from junction 51 to 70, say, in Fig. l through therectifying layer. The arrangement is shown in Figure 3.

What I claim is:

l. An electroluminescent image-producing device cornprising anelectroluminescent phosphor layer, a series of conductive lines on oneside `of said layer, another series of conductive lines on the otherside of said layer, said series being insulated from each other and theprojection of one series lof lines upon the other being at an anglethereto, and a rectifier connected to each of the lines in at least oneof said series.

2. The combination of claim l, and a delay line connected to said oneseries of lines through said rectifier, different wires in the seriesbeing connected to different points on the delay line so that a pulsealong the line will reach them sequentially, a second delay lineconnected to said other series of lines, in the same sequential manner,a terminal of one delay line being connected to a terminal of the otherdelay line through means for producing a signal voltage in seriestherewith.

3. The combination of claim 2, in which the pulse delay produced by `onedelay line is as large as the time required for the pulse along theother delay line to travel along the whole series of conductorsconnected to that line.

4. The combination of claim 3, in which a bias voltage is connected inseries with the delay lines and in which the sum of the pulse voltagesis approximately equal to the bias voltage.

5. An electroluminescent image-producing device comprising anelectroluminescent phosphor layer, a transparent electrically-conductivelayer on one side thereof, and a rectifying layer on the other sidethereof.

6. In combination, first and second series of parallel separatedelectrical conductors, the first-series conductors being oriented at anangle with respect to the second-series conductors, the projection ofeach first-series conductor crossing over each second-series conductorto define a cross-over point thereat, the cross-over points defined byall rst-series conductors and any one second-series conductorconstituting a set of crossover points, the number lof setscorresponding to the number of said secondseries conductors; an electriccircuit associated with each point and interconnecting the rst andsecond series of conductors defining said each point, said circuitincluding in serial connection a rectier and an electroluminescentlayer.

7. The combination of claim l in which the rectifier is connected toeach `of the lines in each of said series.

8. The combination of claim 6 in which the rectifier is a rectifyinglayer.

9. The combination of claim 6 in which the rectier is a rectifying layerand in which the electroluminescent layer includes an electroluminescentphosphor embedded in a dielectric material.

References Cited in the tile of this patent

1. AN ELECTROLUMINESCENT IMAGE-PRODUCING DEVICE COMPRISING ANELECTROLUMINESCENT PHOSPHOR LAYER, A SERIES OF CONDUCTIVE LINES ON ONESIDE OF SAID LAYER, ANOTHER SERIES OF CONDUCTIVE LINES ON THE OTHER SIDEOF SAID LAYER, SAID SERIES BEING INSULATED FROM EACH OTHER AND THEPROJECTION